Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D305/00—Heterocyclic compounds containing four-membered rings having one oxygen atom as the only ring hetero atoms
  • C07D305/14—Heterocyclic compounds containing four-membered rings having one oxygen atom as the only ring hetero atoms condensed with carbocyclic rings or ring systems

Definitions

• the present invention is directed to intermediates useful in the production of the anti-neoplastic compound paclitaxel. More particularly, it is directed to the C-7 metal alkoxides of baccatin III and analogs thereof, as well as methods of producing the same.
• Taxanes are known to exhibit anti-tumor activity. As a result of this activity, taxanes have received increasing attention in the scientific and medical community. Primary among these is a compound known as “paclitaxel” which is also referred to in the literature as “taxol”. Paclitaxel has been approved for the chemotherapeutic treatment of several different varieties of tumors, and the clinical trials indicate that paclitaxel promises a broad range of potent anti-leukemic and tumor-inhibiting activity. Paclitaxel has the formula:
• Paclitaxel is a naturally occurring taxane diterpenoid which is found in several species of the yew (genus Taxus, family Taxaceae). Unfortunately, the concentration of this compound is very low. The species of evergreen are also slow growing. Even though the bark of the yew trees typically exhibit the highest concentration of paclitaxel, the production of one kilogram of paclitaxel requires approximately 16,000 pounds of bark. Thus, the long term prospects for the availability of paclitaxel through isolation are discouraging.
• paclitaxel in the yew tree While the presence of paclitaxel in the yew tree is in extremely low concentrations, there are a variety of other taxane compounds, such as Baccatin III, cephalommanine, 10-deacetylbaccatin III, etc., which are also able to be extracted from the yew bark. Some of these other taxane compounds are more readily extracted in higher yields. Indeed, a relatively high concentration of 10-deacetylbaccatin III can be extracted from the leaves of the yew as a renewable resource.
• taxane compounds such as Baccatin III, cephalommanine, 10-deacetylbaccatin III, etc.
• paclitaxel is synthesized by joining C7-TES baccatin III with N-carbamate protected C2' hydroxyl benzyl- type protected (2R,3S)-3-phenylisoserine, where the C2' hydroxyl is protected by a hydrogenable benzyl-type group such as benzyloxymethyl (BOM) or benzyl. Following the esterification of the protected baccatin III and the protected side chain, the compound may be suitably deprotected, acylated, and further deprotected to yield paclitaxel.
• BOM benzyloxymethyl
• C7-CBZ baccatin III is esterified with a C3'-N-CBZ-C2'-0-protected (2R,3S)-3-phenylisoserine side chain, followed by deprotection to produce paclitaxel.
• That patent teaches that C7-CBZ baccatin III is produced by adding n-butyl lithium and benzyl chloroformate (CBZ-CI) to baccatin III.
• C7-CBZ baccatin III may be directly synthesized from 10-deacetylbaccatin III by adding n-butyl lithium, acetyl chloride (or acetic anhydride) and benzyl chloroformate.
• the present invention is directed to the synthesis of C-7 CBZ protected baccatin III and analogs thereof through a metal alkoxide intermediate.
• the C-7 CBZ protected baccatin III can then be esterified with a suitably protected side chain, then the resulting compound deprotected to yield paclitaxel or other analogs.
• the present invention thus is directed to a new chemical intermediate having the formula
• R is an alkyl group and M + is an alkali metal counterion selected from the group consisting of a potassium counterion and a sodium counterion.
• M + is an alkali metal counterion selected from the group consisting of a potassium counterion and a sodium counterion.
• the alkyl group is a methyl group.
• the present invention is further directed to a method of producing a compound having the above formula, wherein R is an alkyl group and the M + counterion is an alkali metal counterion selected from the group consisting of a potassium counterion and a sodium counterion, from a starting compound which is either baccatin III or 10-deacetylbaccatin III.
• the method comprises the steps of dissolving the starting compound in a first solvent to form a first solution which is then cooled to a temperature of -20°C or less.
• An alkali base selected from the group consisting of a potassium base and a sodium base is thereafter added to the first solution to form an intermediate compound having a metal alkoxide at the C-7 position. Any of the intermediate compound present in the first solution where the intermediate compound does not already have an acetyl group at the C-10 position is then selectively acylated at the C-10 position.
• the starting compound is dissolved in tetrahydrofuran (THF), and the first solution is cooled under a nitrogen atmosphere.
• the alkali base is preferably potassium hydride or sodium hydride.
• the starting compound is 10-deacetylbaccatin III, it is preferred that at least two equivalents of the alkali base is added.
• the first solution is stirred for approximately five minutes.
• the intermediate compound is selectively acylated by adding an acid chloride, preferably acetyl chloride, or acetic anhydride.
• a quenching agent preferably ammonium chloride, may be added to remove excess alkali base and acylating agent.
• the preferred method is conducted so as to produce a compound wherein R is a methyl group.
• the present disclosure is broadly directed to new chemical compounds, namely, C-7 metal alkoxides of baccatin III and analogs thereof.
• the invention also concerns a method of producing these chemical compounds. Such compounds are demonstrably useful for the efficient production of paclitaxel and paclitaxel analogs. More specifically, the present invention discloses C-7 metal alkoxides of baccatin III as useful intermediates in the synthesis of C-7 CBZ baccatin III, which is a useful intermediate in the production of paclitaxel.
• the C-7 CBZ baccatin III may be esterified with an N-CBZ-3-phenylisoserine acid having a hydrogenable benzyl-type hydroxyl protecting group at C-2' to join the side chain at the C-13 hydroxyl of the protected baccatin III backbone.
• the general processes described herein involve the production of the C-7 CBZ baccatin III backbone through the C-7 metal alkoxide intermediate, the condensation of the C-7 CBZ baccatin III backbone with a suitably protected N-CBZ-3-phenylisoserine acid having the hydrogenable benzyl-type protecting group at C-2', and the subsequent deprotection to yield paclitaxel.
• baccatin III can be protected at the C-7 site to yield C-7 CBZ baccatin III.
• 10- deacetylbaccatin III (10-DAB) can be directly converted to C-7 CBZ baccatin III without going through a baccatin III intermediate. Production from baccatin III is advantageous for its yield and simplicity.
• Baccatin III is dissolved in anhydrous THF (tetrahydrofuran) to form a first solution, which is cooled under a nitrogen atmosphere to a reduced temperature of less than -20° C.
• An alkali base such as potassium hydride or sodium hydride (1.6 M in hexane) is then added dropwise to the first solution to form a second solution, which is stirred for approximately five minutes at the reduced temperature. This creates the C-7 metal alkoxide of baccatin
• Benzyl chloroformate (CBZ-CI) is added dropwise to the second solution to form a third solution which is then stirred and allowed to warm to 0° C over approximately one hour.
• the third solution is quenched with cold saturated ammonium chloride to eliminate any excess alkali base and CBZ-CI, and the mixture is concentrated under vacuum to yield a first residue.
• This first residue is next taken up in ethyl acetate and washed once with water to remove unwanted salts. Next, the residue is washed with brine. The organic layer is then dried and concentrated under vacuum to yield a second residue.
• the second residue is recrystallized or column chromatographed with ethyl acetate: hexane to give C-7 CBZ baccatin III as a white solid.
• C-7 CBZ baccatin III can be synthesized directly from 10- deacetylbaccatin III as follows:
• 10-DAB is dissolved in THF to form a first solution which is cooled to a reduced temperature of less than -20° C under a nitrogen atmosphere.
• At least two equivalents of an alkali base such as potassium hydride or sodium hydride (1.6 M in hexane) — or another alkali base, as described above — are then added dropwise to the first solution to form a second solution which is then stirred for approximately five minutes at the reduced temperature.
• acetyl chloride one equivalent
• acetic anhydride one equivalent may possibly be used in place of the acetyl chloride to acylate the 10-DAB.
• benzyl chloroformate (one equivalent) is next added, and this fourth solution is stirred for an additional thirty minutes at the reduced temperature and then warmed to 0° C over thirty minutes.
• the fourth solution is then quenched with cold saturated ammonium chloride at the reduced temperature to remove any excess alkali base, acetyl chloride and CBZ-CI; this mixture is then warmed to room temperature.
• the solvent is removed under vacuum to yield an initial residue which is taken up in ethyl acetate and washed with water to remove unwanted salts. The residue is then washed with brine, dried and concentrated under vacuum to yield a final residue.
• M + K + or Na +
• R is CH 3 or another alkyl group.
• both Route 1 and Route 2 to the production of C-7 CBZ baccatin III can be expressed as a generalized method.
• This method starts with a step of dissolving a starting compound selected from a group consisting of baccatin III and 10-deacetylbaccatin III in a first solvent to form a first solution.
• the first solution is then cooled to a temperature of -20°C or less.
• an alkali base is added to the first solution thereby to form an intermediate compound having a metal alkoxide at the C-7 position thereof.
• the method includes selectively acylating, at the C-10 position, any of the first intermediate compound present in the first solution where the intermediate compound does not already have an acetyl group at the C-10 position thereby to produce a second solution of C-7 metal alkoxide of baccatin III.
• the first intermediate compound may be acylated with the appropriate acid chloride to form analogues with various alkyl groups at C-10.
• the method may include a step of thereafter adding CBZ-CI to the second solution to form a third solution of C-7 CBZ baccatin III.
• the Pi protecting group on the C-2' hydroxyl is a hydrogenatable protecting group such as benzyloxymethyl (BOM) or benzyl.
• the solution is cooled to room temperature and an equal volume of ethyl acetate or diethyl ether is added to the solution.
• the resulting mixture is then cooled to 0°C and held at this temperature for twenty-four hours. After this time it is filtered, and the residue is rinsed with either diethyl ether or ethyl acetate.
• the combined organics are then washed with hydrochloric acid (5%), water, and finally brine.
• the organic phase is separated, dried and concentrated under vacuum.
• the resulting residue is then dissolved in ethyl acetate: hexane and eluted over a silica gel plug. The eluent is then concentrated under vacuum to result in the esterified compound:
• the esterified compound, above, may now be converted into paclitaxel by removing the nitrogen and C-7 CBZ groups, putting the benzoyl group onto the nitrogen, and finally removing the C-2' benzyl-type protecting group. Removal of the CBZ groups, and subsequent addition of the benzoyl group to the nitrogen are accomplished as follows (BOM is shown as the protecting group at the C-2' hydroxyl site, although benzyl could also be used):
• the coupled product is dissolved in isopropanol to which the Pearlman's catalyst is added.
• the resulting mixture is hydrogenated at 40 psi for twenty-four hours, although alternatively, the mixture can be stirred under one atmosphere of hydrogen for twenty-four hours.
• the mixture is filtered through diatomaceous earth and reduced under vacuum to residue.
• the residue is taken up in toluene and anhydrous potassium carbonate added.
• the residue may be taken up in ethyl acetate or toluene and a tertiary amine base, such as triethylamine, is added.
• benzoyl chloride is then added dropwise, and the mixture stirred for two hours.
• the resulting mixture is then washed with water and finally brine.
• the resulting organic phase is then separated, dried, and concentrated under vacuum to yield C-2' BOM paclitaxel.
• the BOM protected paclitaxel is dissolved in isopropanol to which Pearlman's catalyst is added. This mixture is hydrogenated for twenty-four hours under 40 psi hydrogen to yield paclitaxel.

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• Chemical & Material Sciences (AREA)
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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
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• 1999
  • 1999-02-19 US US09/252,739 patent/US5973170A/en not_active Expired - Fee Related
• 2000
  • 2000-02-18 EP EP00915802A patent/EP1155008A4/en not_active Withdrawn
  • 2000-02-18 RU RU2001125669/04A patent/RU2001125669A/ru unknown
  • 2000-02-18 WO PCT/US2000/004271 patent/WO2000049006A1/en not_active Application Discontinuation
  • 2000-02-18 IL IL14459100A patent/IL144591A0/xx unknown
  • 2000-02-18 AU AU37016/00A patent/AU3701600A/en not_active Abandoned
  • 2000-02-18 CZ CZ20012786A patent/CZ20012786A3/cs unknown
  • 2000-02-18 CN CNB008038716A patent/CN1148363C/zh not_active Expired - Fee Related
  • 2000-02-18 KR KR1020017010480A patent/KR20010102234A/ko not_active Application Discontinuation
  • 2000-02-18 JP JP2000599746A patent/JP2003518004A/ja active Pending
  • 2000-02-18 CA CA002361922A patent/CA2361922A1/en not_active Abandoned
  • 2000-02-18 MX MXPA01008352A patent/MXPA01008352A/es not_active Application Discontinuation
  • 2000-02-18 BR BR0008352-6A patent/BR0008352A/pt not_active Application Discontinuation
• 2001
  • 2001-08-03 ZA ZA200106383A patent/ZA200106383B/xx unknown
  • 2001-08-14 NO NO20013935A patent/NO20013935L/no not_active Application Discontinuation

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